This invention relates to a method for producing a polyolefin by polymerizing at least one olefin in the presence of a novel catalyst system. More particularly, this invention relates to a method whereby a polyolefin having excellent quality can be produced in a single catalyst system at high productivity and high catalytic activity irrespective of the range of density and the method of production.
It is already known to use a catalyst system comprising a transition metal compound and an organometallic compound for low-pressure polymerization of olefins, and such system is widely employed on an industrial scale.
With respect to polyolefins obtainable by the low-pressure polymerization of olefins, it is known that by controlling the density, a wide range of polyolefins can be produced ranging from those having a relatively low density and being excellent in transparency and flexibility, for example, a linear low-density polyethylene, to those having a high density and being excellent in stiffness, for example, a high-density polyethylene and an isotactic polypropylene. For catalyst systems suitable therefore, various studies have been made from various aspects in industry and universities, and many proposals have been made.
On the other hand, as the low-pressure polymerization method using the above catalyst system, there have been known a method, such as a slurry polymerization method, which employes a solvent and thus has an advantage that removal of by-products can be done by the solvent, and a gas-phase polymerization method which employs no solvent and is advantageous from the viewpoint of energy. Industrial productivity in each polymerization method depends substantially on the quality of the resulting polyolefin and the properties of polyolefin particles. More specifically, if the bulk density, average particle size, particle size distribution, proportion of fine particles, and the like of the resulting polyolefin particles are not satisfactory, process troubles are likely to result thereby reducing the productivity. Thus, many proposals have already been made for improving the particle properties with respect to catalyst systems suitable for the respective polymerization methods.
However, conventional proposals are concerned with the technology for the combination of a specific range of density and a specific polymerization method. Therefore, to satisfy the diversification of polyolefins in the market in recent years, polyolefin producers are required to appropriately select and use suitable catalyst systems depending on the respective combinations of the range of density and the polymerization method. That is, in such conventional technology, they must have various catalyst systems to satisfy the diversification of the range of density and the diversification of the polymerization method, such being disadvantageous from the industrial viewpoint.
Under such circumstances, the present inventors have made a further study to make it possible to produce polyolefins of every range of density with a single catalyst system by an optional polymerization method.
For example, in Japanese Examined Patent Publication No. 15110/1977, the present inventors have proposed a catalyst system which exhibits quite high catalytic activities and which comprises a catalyst component (A) obtained by reacting magnesium metal and a hydroxylated organic compound, or an oxygen-containing organic compound of magnesium, an oxygen-containing organic compound of a transition metal and an aluminum halide, and a catalyst component (B) of an organometallic compound. However, when such a catalyst system is applied to a slurry polymerization method or a gas phase polymerization method, polymer particles obtained are still not satisfactory in the powder properties because the average particle size is small, the particle size distribution is broad, and the proportion of fine particles contained in the polymer particles is high.
The present inventors have previously found that the particle size of a polymer can be increased by using a silicon compound in addition to the raw materials for a catalyst component (A) disclosed in Japanese Examined Patent Publication No. 15110/1977, and filed a patent application i.e. Japanese Examined Patent Publication No. 58367/1987, but such a method has not led to an improvement in the particle size distribution.
Further, the present inventors have found that the particle size distribution can be improved by partially reducing raw materials for a catalyst component (A) disclosed in Japanese Examined Patent Publication No. 15110/1977 with an organoaluminum compound, followed by a reaction with a silicon compound and further with an aluminum halide compound, and filed a patent application i.e. Japanese Unexamined Patent Publication No. 262802/1985. However, in this method, the particle size is not sufficiently large and the catalyst particles tend to disintegrate during the step of transportation or polymerization. In addition, in a gas phase polymerization, not only the polymer tends to be fine powder, but also the catalytic activity tends to be low, whereby there still remains a room for improvement.
Under such circumstances, several solutions for improving the particle properties have been proposed. For example, in Japanese Examined Patent Publication No. 49026/1977, it is proposed to conduct a so-called prepolymerization by activating a halide of a trivalent titanium with an organoaluminum compound, followed by treatment with an olefin having from 2 to 6 carbon atoms. However, in this method, the catalytic activity is insufficient and the properties of polyolefin particles are not satisfactory.
Under such circumstances, the present inventors have conducted a gas phase polymerization by applying the technology of this prepolymerization to the catalyst as disclosed in Japanese Unexamined Patent Publication No. 262802/1985. However, as shown in Comparative Examples, both the activity and the powder properties are not satisfactory.
That is, the technique of prepolymerization is not universally effective for any optional catalyst system. In this connection, for example, Japanese Unexamined Patent Publication No. 219311/1984 discloses that when a solid state transition metal catalyst comprising, as essential components, magnesium, a transition metal and a halogen, is prepolymerized with xcex1-olefin, the catalyst tends to be fine particles, and the polymer thereby obtained, accordingly tends to be fine powder. This publication shows that the technology of prepolymerization exhibits a specific effect to a specific catalyst.
An object of the present invention is to make it possible to produce polyolefins of various ranges of density at high productivity by a single catalyst system by an optional polymerization method. More specifically, the object is to provide a method capable of producing polyolefins ranging from a high density to a low density at high catalytic activity by the slurry polymerization method or the gas phase polymerization method, whereby excellent polyolefin particles having a high bulk density, a narrow particle size distribution and a large particle size can be produced.
The present invention have conducted extensitve researches to attain the above-mentioned object, and, as a result, have found it possible to obtain a polymer excellent in powder properties such as bulk density, particle size distribution or particle size by a slurry polymerization method or a gas phase polymerization method by combining an organometallic compound and a solid catalyst component obtained by prepolymerizing at least one xcex1-olefin to a solid composite having a specific composition. The present invention has been accomplished on the basis of this discovery.
The present invention provides a method for producing a polyolefin, which comprises polymerizing at least one xcex1-olefin in the presence of a catalyst system comprising:
(A) a solid catalyst component prepared by prepolymerizing
(vi) at least one xcex1-olefin in the presence of a solid composite obtained by reacting a homogeneous solution containing
(i) at least one member selected from the group consisting of metal magnesium and a hydroxylated organic compound, and oxygen-containing organic compounds of magnesium,
(ii) at least one oxygen-containing organic compound of titanium and
(iii) at least one silicon compound, with
(iv) at least one organoaluminum halide compound, and
(v) at least one member selected from the group consisting of organometallic compounds of metals of Groups Ia, IIa, IIb, IIIb and IVb of the Periodic Table, and
(B) at least one member selected from the group consisting of organometallic compounds of metals of Groups Ia, IIa, IIb, IIIb and IVb of the Periodic Table.
Now, the present invention will be described in detail with reference to the preferred embodiments.
Metal magnesium and a hydroxylated organic compound, and oxygen-containing organic compounds of magnesium that are used as reactant (i) in the present invention will be described below.
Firstly, when metal magnesium and a hydroxylated organic compound are used, metal magnesium can take any form such as powdery form, granular form, foil form, or ribbon form, and as the hydroxylated organic compound, alcohols, organosilanols, and phenols are suitable.
As the alcohols, linear or branched aliphatic alcohols, alicyclic alcohols, aromatic alcohols having 1 to 18 carbon atoms can be used. Specific examples include methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, n-hexanol, 2-ethylhexanol, n-octanol, i-octanol, n-stearyl alcohol, cyclopentanol, cyclohexanol, and ethylene glycol.
The organosilanols are those having at least one hydroxyl group and an organic group selected from an alkyl group, a cycloalkyl group, an arylalkyl group, an aryl group, and an alkylaryl group with 1 to 12, preferably 1 to 6, carbon atoms. For example, trimethylsilanol, triethylsilanol, triphenylsilanol, and t-butyldimethylsilanol may be mentioned.
As phenols, phenol, cresol, xylenol, and hydroquinone may be mentioned.
These hydroxylated organic compounds can be used alone or as a mixture of two or more of them. They may be, of course, used alone, but, when they are used as a mixture of two or more of them, such a mixture may sometimes present a unique effect to powder properties or the like of a polymer.
In addition, when metal magnesium is used to prepare a solid catalyst composite of the present invention, for the purpose of accelerating the reaction, it is preferable to add one or more substances that will react or form an adduct, with metal magnesium, e.g. polar substances such as iodine, mercuric chloride, halogenated alkyls, organic acid esters, and organic acids.
As compounds belonging to the oxygen-containing organic compounds of magnesium, the following compounds may, for example, be mentioned: magnesium alkoxides such as magnesium methylate, magnesium ethylate, magnesium isopropylate, magnesium decanolate, magnesium methoxyethylate and magnesium cyclohexanolate, magnesium alkylalkoxides such as magnesium ethylethylate, magnesium hydroalkoxides such as magnesium hydroxymethylate, magnesium phenoxides such as magnesium phenate, magnesium naphthenate, magnesium phenanthlenate and magnesium cresolate, magnesium carboxylates such as magnesium acetate, magnesium stearate, magnesium benzoate, magnesium phenylacetate, magnesium adipate, magnesium sebacate, magnesium phthalate, magnesium acrylate and magnesium oleate, magnesium oxymates such as magnesium butyloxymates, magnesium dimethylglyoxymates and magnesium cyclohexyloxymate, magnesium hydroxamate salts, magnesium hydroxylamine salts such as N-nitroso-N-phenyl-hydroxylamine derivatives, magnesium enolates such as magnesium acetylacetonate, magnesium silanolates such as magnesium triphenyl silanolate, and complex alkoxides of magnesium and other metals, such as, Mg[Al(OC2H5)4]2. These oxygen-containing organic magnesium compounds are used alone or as a mixture of two or more of them.
As the oxygen-containing organic compound of titanium for the above-mentioned reactant (ii), a compound represented by the general formula [TiOa(OR1)b]m is used, in which R1 represents a hydrocarbon group such as a linear or branched alkyl group, a cycloalkyl group, an arylalkyl group, an aryl group, and an alkylaryl group, having 1 to 20, preferably 1 to 10, carbon atoms, a and b are such that axe2x89xa70 and b greater than 0 and they are numbers agreeable with the valence of titanium, and m is an integer. It is particularly preferred to use an oxygen-containing organic compound in which a is 0xe2x89xa6axe2x89xa61 and m is 1xe2x89xa6mxe2x89xa66.
As specific examples, titanium tetraethoxide, titanium tetra-n-propoxide, titanium tetra-i-propoxide, titanium tetra-n-butoxide and hexa-i-propoxy dititanate may be mentioned. Use of an oxygen-containing organic compound having different hydrocarbon groups falls within the scope of the present invention. These oxygen-containing organic compounds are used alone or as a mixture of two or more of them.
As the silicon compound for the reactant (iii), the following polysiloxanes and silanes may be used.
As polysiloxanes, siloxane polymers of a linear, cyclic or three-dimensional structure may be mentioned which have repeating units of one or more types of the general formula:
xe2x80x94(Si(R2)(R3)xe2x80x94Oxe2x80x94)pxe2x80x94
wherein R2 and R3 may be the same or different and each represents an atom or a residual group that can bond to the silicon, for example, a hydrocarbon group such as an alkyl group or an aryl group, having from 1 to 12 carbon atoms, hydrogen, a halogen, or an alkoxy group, an aryloxy group or a fatty acid residue, having from 1 to 12 carbon atoms, and p is usually an integer of from 2 to 10,000, in various proportions and distributions in the molecule, except for the case where R2 and R3 are all hydrogen or halogen.
Specifically, the linear polysiloxanes may, for example, be hexamethyldisiloxane, octamethyltrisiloxane, dimethylpolysiloxane, diethylpolysiloxane, methylethylpolysiloxane, methylhydropolysiloxane, ethylhydropolysiloxane, butylhydropolysiloxane, hexaphenyldisiloxane, octaphenyltrisiloxane, diphenylpolysiloxane, phenylhydropolysiloxane, methylphenylpolysiloxane, 1,5-dichlorohexamethyltrisiloxane, 1,7-dichlorooctamethyltetrasiloxane, dimethoxypolysiloxane, diethoxypolysiloxane, and diphenoxypolysiloxane.
The cyclic polysiloxanes may, for example, be hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, 2,4,6-trimethylcyclotrisiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, triphenyltrimethylcyclotrisiloxane, tetraphenyltetramethylcyclotetrasiloxane, hexaphenylcyclotrisiloxane, and octaphenylcyclotetrasiloxane.
The polysiloxanes having a three-dimensional structure may, for example, be those obtained by heating the above linear or cyclic polysiloxanes to let them have a crosslinked structure.
These polysiloxanes are preferably liquid for the convenience in handling, and it is desirable that they have a viscosity within a range of from 1 to 10,000 centistokes, preferably from 1 to 1,000 centistokes, at 25xc2x0 C. However, they are not necessarily limited to liquid polysiloxanes, and they may be solid that are generally called silicon grease.
The silanes may, for example, be compounds represented by the general formula HqSirR4sXt wherein R4 represents a group that can bond to the silicon, for example, a hydrocarbon group such as an alkyl group or an aryl group, having from 1 to 12 carbon atoms, or an alkoxy group, an aryloxy group or a fatty acid residue, having from 1 to 12 carbon atoms, and the plurality of R4 may be the same or different; the plurality of X may be the same or different and each represents a halogen; each of q, s and t is an integer of 0 or more, r is a natural number, and q+s+t=2r+2 or 2r.
Specifically, they include, for example, silanhydrocarbons such as trimethylphenylsilane, dimethyldiphenyldisilane and allyltrimethylsilane, linear and cyclic organic silanes such as hexamethyldisilane and octaphenylcyclotetrasilane, organic silanes such as methylsilane, dimethylsilane and trimethylsilane, silicon halides such as silicon tetrachloride and silicon tetrabromide, alkyl and aryl halogenosilanes such as dimethyldichlorosilane, diethyldichlorosilane, n-butyltrichlorosilane, diphenyldichlorosilane, triethylfluorosilane and dimethyldibromosilane, alkoxysilanes such as trimethylmethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, tetramethoxysilane, tetraethoxysilane, diphenyldiethoxysilane, tetramethyldiethoxydisilane and dimethyltetraethoxydisilane, haloalkoxysilanes and halophenoxysilanes such as dichlorodiethoxysilane, dichlorodiphenylsilane and tribromoethoxysilane and silane compounds containing a fatty acid residue such as trimethylacetoxysilane, diethyldiacetoxysilane and ethyltriacetoxysilane.
Preferred are linear polysiloxanes such as dimethylpolysiloxane and methylhydropolysiloxane, and alkoxysilanes such as methyltrimethoxysilane, tetramethoxysilane and tetraethoxysilane.
The above organosilicon compounds may be used alone or two or more of them may be mixed or reacted for use.
As the organoaluminum halide compound for the reactant (iv), those represented by the general formula AlR5zX3xe2x88x92z may be used. In the formula, R5 represents a hydrocarbon group having from 1 to 20, preferably 1 to 8, carbon atoms, X represents a halogen atom, and z is such a number that 0 less than z less than 3, preferably 0 less than zxe2x89xa62. R5 is preferably selected from a linear or branched alkyl group, a cycloalkyl group, an arylalkyl group, an aryl group and an alkylaryl group.
Specific examples of the organoaluminum halide compound include dimethylaluminum chloride, diethylaluminum chloride, diethylaluminum bromide, dipropylaluminum chloride, ethylaluminum dichloride, i-butylaluminum dichoride, methylaluminum sesquichloride, ethylaluminum sesquichloride, i-butylaluminum sesquichloride, and a mixture of triethylaluminum and aluminum trichloride.
The above organoaluminum halide compounds may be used alone or as a mixture of two or more of them. It is preferred to use a mixture of two or more of them for good powder properties.
When the solid catalyst of the present invention is prepared, the order of reacting the reactants (i), (ii) and (iii) may be any desired order so long as the chemical reactions can be carried out. For example, there may be mentioned a method wherein a silicon compound is added to a mixture of a magnesium compound and a titanium compound, a method wherein a magnesium compound, a titanium compound and a silicon compound are mixed at the same time, a method wherein a titanium compound is added to a magnesium compound and a silicon compound. A homogeneous Mgxe2x80x94Ti solution containing a silicon compound can be obtained by such method.
Then, a solid composite to be used in the present invention can be obtained by adding the reactant (iv) to this Mgxe2x80x94Ti solution.
These reactions are preferably conducted in a liquid medium. Therefore, when these reactants are not liquid by themselves under the operating conditions, or when the amount of liquid reactants is not sufficient, the reaction should be conducted in the presence of an inert organic solvent. As such an inert organic solvent, any solvent which is commonly used in this technical field may be employed. As the solvent, an aliphatic, alicyclic or aromatic hydrocarbon or a halogen derivative thereof, or a mixture thereof may be mentioned. For example, isobutane, hexane, heptane, cyclohexane, benzene, toluene, xylene or monochlorobenzene may be preferably used.
The amounts of the reactants to be used in this invention are not particularly limited, but the atomic ratio of the gram atom of Mg in the magnesium compound of the above (i) to the gram atom of Ti in the titanium compound of the above (ii), is usually 1/20xe2x89xa6Mg/Tixe2x89xa6100, preferably 1/5xe2x89xa6Mg/Tixe2x89xa610. If the ratio is outside this range and Mg/Ti is too large, it tends to be difficult to obtain a homogeneous Mgxe2x80x94Ti solution at the time of preparation of the catalyst, or the activity of the catalyst tends to be low at the time of polymerization. If the ratio is inversely too small, problems may arise such that the catalytic activity tends to be low and the product is colored.
It is preferred to select the amounts so that the atomic ratio of the gram atom of Si in the silicon compound of the above (iii) to the gram atom of Mg in the magnesium compound of the above (i), will be usually 1/20xe2x89xa6Mg/Sixe2x89xa6100, preferably 1/10xe2x89xa6Mg/Sixe2x89xa610. If the ratio is outside this range and Mg/Si is too large, the improvement of powder properties will sometimes be insufficient. If the ratio is inversely too small, the catalytic activity tends to be low. In the present invention, the type and amount of the organoaluminum halide of the above (iv) are properly selected, and when a solid composite is to be precipitated in the homogeneous Mgxe2x80x94Ti solution, it is common to appropriately control formation of crystalline nuclei, especially at the initial stage of the reaction. The reaction of the Mgxe2x80x94Ti solution and the reactant (iv) may be conducted in one step, but particularly preferably in two separate steps. That is, when the reaction is separated in two steps, precipitation of the crystalline nuclei is conducted in the first step, and growth of the crystalline nuclei precipitated in the first step, is conducted in the second step. Thus, it is required to select the types and amounts of the reactants (iv) to be used in the first and second steps so that they would be suitable to the respective steps. More specifically, it is preferred that, in the reaction of the first step, z of R5zAlX3xe2x88x92z is 1xe2x89xa6zxe2x89xa62, and its amount (molar ratio) to Mg is from 0.1 to 2.5, and in the reaction of the second step, they are 0 less than z less than 2 and from 0.5 to 20, respectively.
The reaction conditions in each step are not particularly limited, and the reaction is carried out usually at the temperature within the range of from xe2x88x9250 to 300xc2x0 C., preferably from 0 to 200xc2x0 C., for 0.5 to 50 hours, preferably for 1 to 6 hours, in an inert gas atmosphere under an ordinary pressure or an elevated pressure.
The solid composite thus obtained may be separated from remaining unreacted substances and by-products by filtration or decantation, or may not be separated therefrom. Then, the solid composite is suspended in an inert organic solvent and subjected to prepolymerization. Prepolymerization is conducted by contacting an xcex1-olefin to the solid composite in the presence of the organometallic compound at the temperature of not higher than 100xc2x0 C. As the xcex1-olefin to be prepolymerized to the solid composite, ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-pentene, 2-methyl-l-pentene, 4-methyl-1-pentene or 1-octene may be mentioned. These xcex1-olefins may be used alone or as a mixture of two or more of them for the prepolymerization to the solid composite.
As the organometallic compounds of Groups Ia, IIa, IIb, IIIb and IVb of the Periodic Table for the above (v), there may be mentioned organometallic compounds comprising a metal such as lithium, magnesium, zinc, tin or aluminum, and an organic group.
As the organic group, an alkyl group may be mentioned as a typical example. As the alkyl group, a linear or branched alkyl group having 1 to 20 carbon atoms may be used. Specifically, n-butyllithium, diethylmagnesium, diethylzinc, trimethylaluminum, triethylaluminum, tri-i-butylaluminum, tri-n-butylaluminum, tri-n-decylaluminum, tetraethyltin or tetrabutyltin, may be mentioned.
It is particularly preferred to use a trialkylaluminum having a linear or branched alkyl group having from 1 to 10 carbon atoms.
In addition, an alkyl metal hydride having an alkyl group having from 1 to 20 carbon atoms may be used as the organometallic compound. As such a compound, there may be specifically mentioned diisobutylaluminum hydride or trimethyltin hydride. There may also be used an alkyl metal halide having an alkyl group having from 1 to 20 carbon atoms such as ethylaluminum sesquichloride, diethylaluminum chloride or diisobutylaluminum chloride, and an alkyl metal alkoxide such as diethylaluminum ethoxide.
There may also be used an organoaluminum compound obtained by the reaction of a trialkylaluminum or dialkylaluminum hydride having an alkyl group having from 1 to 20 carbon atoms with a diolefin having from 4 to 20 carbon atoms, such as isoprenylaluminum.
The above organometallic compounds may be used alone, or two or more of them may be mixed or reacted for use. Further, an electron donative compound may be used for the purpose of controlling the molecular weight and stereospecificity.
When the electron donative compound is to be used, it is proper to use as such compound, an organic acid ester, an oxygen-containing organic compound of silicon, or a nitrogen-containing organic compound. Specifically, ethylbenzoate, ethyltoluylate, tetraethoxysilane, diphenyldimethoxysilane and diphenylamine may be mentioned.
The total amount of the xcex1-olefin to be used for the prepolymerization is preferably within the range of from 0.001 to 20 parts by weight, particularly preferably from 0.01 to 10 parts by weight, per part by weight of the solid composite. If the absorbed amount of xcex1-olefin is too small, the particle size of the catalyst tends to be insufficient, and if the absorbed amount is too large, the solid composite particles sometimes adhere to one another. This contacting treatment may be conducted in a gas phase or without a solvent, or may be conducted in the presence of an inert organic solvent. When the treatment is conducted in the presence of the inert organic solvent, said organic solvent may be the same as the one used for the preparation of the solid composite.
The contacting conditions are not particularly limited, but it is required to conduct the contacting under the conditions substantially free from oxygen and moisture. In general, this contacting treatment may be carried out within a temperature range of from xe2x88x9250 to 100xc2x0 C., preferably from 0 to 50xc2x0 C., under an ordinary pressure or an elevated pressure. It is preferred to carry out the contact sufficiently under a flowing state when the treatment is conducted in a gas phase, or under stirring when the treatment is conducted in a liquid phase.
The amount of the solid composite to be used is not particularly limited, but it may preferably be used in an amount of from 0.1 to 500 g per liter of the solvent or per liter of the reactor. The amount of the organometallic compound to be used is selected from the range of from 0.1 to 200 mol per mol of Ti of the solid composite, and when the electron donative compound is used, the amount is selected from the range of from 0.1 to 10 mol per mol of the organometallic compound.
After the prepolymerization, the resulting catalyst component may be washed with an inert organic solvent, or such washing may be omitted.
The catalyst component (A) thus obtained may be used as such in the suspended condition for polymerization, but as the case requires, it may be separated from the solvent, or it may be dried by heating under an ordinary pressure or a reduced pressure to remove the solvent and used in such a dried state.
In the present invention, the organometallic compound for the catalyst component (B) may be the same as the organic compound of the above (v).
The polymerization of olefins according to the present invention can be carried out under usual reaction conditions of a so-called Ziegler process. That is, polymerization can be conducted at a temperature of from 20 to 110xc2x0 C. by a continuous system or a batch system. The polymerization pressure is not particularly limited, but it is suitable to employ an elevated pressure, particularly from 1.5 to 50 kg/cm2 G. When the polymerization is carried out in the presence of an inert solvent, as the inert solvent, any one usually employed can be used. Particularly, it is proper to use an alkane or cycloalkane having from 4 to 20 carbon atoms, for example, isobutane, pentane, hexane or cyclohexane.
When the polymerization is carried out in a gas phase, the reactor to be used for the polymerization steps may be of any type which is commonly used in this technical field, for example, a fluidized bed reactor or a stirring tank type reactor. When the fluidized bed reactor is used, the reaction is conducted by blowing an olefin in the gas state and/or an inert gas into the reaction system, thereby maintaining the reaction system in the state of fluid. As a stirrer when the stirring tank type reactor is used, various type of stirrers can be employed, for example, an anchor type stirrer, a screw type stirrer, a ribbon type stirrer and the like.
The polymerization of the present invention includes not only homopolymerization of an xcex1-olefin but also copolymerization of two or more xcex1-olefins. As the xcex1-olefin to be used for the polymerization, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene or 4-methyl-1-pentene, may, for example, be mentioned. Also, copolymerization can be conducted by using a mixture of an xcex1-olefin and a diene such as butadiene or isoprene to introduce double bond into the polymer. It is necessary to select the amount of the xcex1-olefin to be used for the copolymerization depending on the desired density of an objective polymer. It is possible to produce the polymer of the present invention within a density range of from 0.890 to 0.970 g/cm3.
The polymerization operation of the present invention can be carried out by not only one stage polymerization which is conducted under a common single polymerization condition, but also multistage polymerization which is conducted under plural polymerization conditions.
In the practice of the present invention, the catalyst component (A) is used preferably in an amount of from 0.001 to 2.5 mmol in terms of titanium atom per liter of the solvent or per liter of the inner volume of the reactor, and depending on the conditions, a higher concentration may be used.
The organoaluminum of the catalyst component (B) is used at a concentration of from 0.02 to 50 mmol, preferably from 0.2 to 5 mmol, per liter of the solvent or per liter of the internal volume of the reactor.
In the present invention, the molecular weight of the produced polymer can be controlled by a conventional means, e.g. a method in which an appropriate amount of hydrogen is present in the reaction system.
A first effect of the present invention resides in that it is possible to produce polyolefins having various ranges of density at high productivity by a single catalyst system by an optional polymerization method. That is, according to the present invention, it is possible to obtain polyolefins ranging from a high density to a low density by a slurry polymerization method or a gas phase polymerization method with a high catalytic activity, and a further to obtain polyolefin particles having excellent properties such as high bulk density, a narrow particle size distribution and a large particle size. Thus, in the polymerization step, formation of substances adhering to the polymerization apparatus can be inhibited. Further, in the transportation step, no bridge will be formed in the silo, and troubles involved in the transportation can be eliminated. Further, granulation can be conducted very smoothly. If the particle size distribution of a polymer is narrow, classification of particles hardly arises and uniform particles can be obtained, particularly in the case of producing a polymer having a wider molecular weight distribution by a multi-stage polymerization method, whereby hard spots or unevenness will not be formed in the product.
The second effect of the present invention is that the catalytic activity is high without impairing powder properties i.e. the weight of a polymer obtainable per unit weight of the catalyst component (A) is remarkably large. Thus, it is not necessary to take a special measure, to remove a catalyst residue from the polymer, and it is possible to avoid problems such as deterioration and coloring of the polymer at the time of molding.
Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted by such specific Examples. In the Examples and Comparative Examples, HLMI/MI stands for the ratio of the high-load melt index (HLMI; measured under the condition F of ASTMD-1238) to the melt index (MI; measured under the condition E of ASTMD-1238), and is an index for the molecular weight distribution. If the HLMI/MI value is small, the molecular weight distribution is considered to be small.
The activity shows the amount (g) of a polymer produced per gram of the solid catalyst component (A). With respect to the width of the particle size distribution of the polymer particles, the results of the classification of the polymer particles by sieves are plotted on a probability logarithmic paper to find the geometric standard deviation from the approximated straight line in known manner, and the width is expressed in terms of its common logarithm (hereinafter referred to as "sgr"). The average particle size is a value obtained by reading the particle size corresponding to the weight accumulated value 50% of the above approximated line.